The present disclosure relates to a gasification process and feed system for the production of synthesis gas by partial combustion of a carbonaceous feed. The disclosure is directed to a feed process and system for supplying the carbonaceous feed to a gasification reactor.
The carbonaceous feed can for instance comprise pulverized coal, biomass, petcoke, or any other type of solid carbonaceous feed or mixture thereof. In particular the carbonaceous feed is supplied as a solid dry feedstock.
Typically, the carbonaceous feed is provided to one or more burners of a gasification reactor, together with an oxygen comprising gas stream and optionally also a moderator gas. In the reactor, the feed is partially oxidized to provide syngas. The syngas is subsequently cooled in a quench section. The cooled syngas is typically treated, for instance to remove contaminants.
Syngas, or synthesis gas, as used herein is a gas mixture comprising hydrogen and carbon monoxide, and some carbon dioxide. The (treated) syngas can be used, for instance, as a fuel, or as an intermediary product for creating synthetic natural gas (SNG) or for producing ammonia, methanol, hydrogen, waxes, synthetic hydrocarbon fuels or oil products, or as a feedstock for other chemical processes.
US2007225382 discloses a process to produce synthesis gas or a hydrocarbon product from a solid carbonaceous fuel in a gasification reactor. The carbonaceous fuel and an oxygen containing stream are supplied to a burner of a gasification reactor, wherein a CO2-containing transport gas is used to transport the solid carbonaceous fuel to the burner. The carbonaceous fuel is partially oxidized in the gasification reactor, to obtain synthesis gas. The synthesis gas can be further processed in a downstream process path, to convert the syngas into a selected hydrocarbon product. The downstream process path may contain a methanol-synthesis reactor to produce the hydrocarbon product, such as methanol. The downstream process path may contain a Fischer-Tropsch synthesis reactor to convert the syngas and allow to produce a selected product from a range of hydrocarbon products.
The environmental regulations governing the emission vent gases from a (coal) gasification plant are becoming ever more strict. One recent issue has arisen for so-called dry-coal feed systems, which use CO2 as an inert gas for coal pressurisation and feeding, such as for instance disclosed in US2007225382. After coal transport into the gasifier, the excess gas used for pressurisation in the so-called lock hopper, sluice hopper, or sluice vessel is vented, after which a new pressurisation cycle starts. The CO2 that is used in this process may be derived from a Rectisol syngas treating plant, which typically uses methanol as an absorbent for CO2 and/or H2S, to remove the latter from the syngas. Consequently, the recycled CO2 may contain methanol up to a concentration which exceeds allowable vent levels, for instance in the order of 300 to 400 ppm (volume).
There are currently hardly any acceptable alternative technologies, since absorbers of methanol rely on water, which then gets absorbed in the CO2 to levels which are unacceptable for dry-feeding of coal. In addition, such absorbers would increase the cost of a coal gasification plant.